Since we'll be adding the ability to ad issues directly from the epic page, it makes sense to add the Epic field here too:

Related: https://gitlab.com/gitlab-org/gitlab-ee/issues/13808

Proposal

• Add Epic option, under Assignee
• User can add an Epic similarly to how they would add an epic from the sidebar
• Push items "down" the list, therefor weight is now in the next column above due date